1. Field of the Invention
The present invention relates to a method for precisely detecting defects such as particles or defective patterns formed on a semiconductor device.
2. Description of the Related Art
In general, as semiconductor devices become more highly integrated, reducing defects such as particles or defective patterns becomes as important as the fabrication processes in order to maximize yield. Therefore, it is important to provide optimal conditions during each unit process to produce fewer defects, and also to exactly monitor any defects formed on the semiconductor wafer during each unit process. Accordingly, various detection devices are used for monitoring defects generated before, during or after each unit process.
In general, the detection devices shine a light on the semiconductor device and measure the intensity of returned light (i.e., scattered or reflected light) to detect defects. After a unit process, defects are monitored on either a test wafer or a production wafer by varying the drive conditions, i.e., the control settings, of a defect detection device as appropriate for that particular unit process (process type or formed film type). The control settings must be varied to optimize the ability of the device to detect defects, because both the character of light returned from correct structures and also the character of light returned from defects vary after different process steps. The control settings of the detection devices must be selected to detect as many actual defects as possible and avoid false detections in which correct structures are classified as defects.
However, it is difficult to select the optimal values for control settings to detect defects of a given type and size; it is also difficult to determine what percentage of defects are being detected, i.e., the detection sensitivity, for a single device; and, more particularly, it is difficult to select the control settings of several devices to obtain comparable detection sensitivities among all the devices.
Although the detection devices are equipped with various functions such as self calibration for the purpose of increasing the expected reliability of detection, experience shows that the actual reliability of detection can deteriorate greatly in spite of such functions.